W5 AT: track changes to project.json

[hirokiterashima]

Description

Track changes made to project.json via the W5 Authoring Tool.

Steps to Reproduce

1. Make changes to the project in AT
2. Save

Expected behavior: a new revision change should be saved.

Actual behavior: no revision is saved.

Additional Information

In the past we had tracked all changes to a project using JGit on the server-side. We disabled this feature because the change history grew too big quickly. We think it's because we were tracking assets. If we only tracked changes to project.json, it should take much less space and we can still get the changes made to the project sans assets.